Russia's ambassador to the United States said Washington had threatened retaliation after Wall Street Journal reporter Evan Gershkovich was detained on espionage charges, and suggested it might be time to cut the number of US journalists in Russia.

Russia's Federal Security Service (FSB) said on March 30 it had detained Gershkovich in the Urals city of Yekaterinburg and had opened an espionage case against him for collecting what it said were state secrets about the military industrial complex.

Gershkovich, the first American journalist detained in Russia on espionage charges since the end of the Cold War, and the Journal have denied he was involved in espionage.

The United States has urged Russia to release Gershkovich and cast the Russian claims of espionage as ridiculous. US President Joe Biden has called for Gershkovich's release.

"The Americans have threatened us with retaliatory measures if we do not release Gershkovich in the near future,” Russian ambassador Anatoly Antonov told Russia's First Channel state television.

“We shall see how they will act.” Antonov said he had had a“very harsh” conversation with US Under Secretary of State Victoria Nuland, who accused Russia of illegally detaining Gershkovich.

Antonov said Nuland had repeatedly interrupted him in a counterproductive way.

The Russian ambassador said that it might be time to reduce the number of American journalists working in Russia. ”The Americans have a very good word - reciprocity which they always insist on,” Antonov told the Bolshaya Igra show.

"Perhaps it is the time for us to show reciprocity and reduce the number of American journalists who work in Moscow and in Russia as a whole to the number [of Russian journalists] who work in Washington and New York,” Antonov said.

The Kremlin said Gershkovich had been carrying out espionage "under the cover” of journalism. Foreign Minister Sergei Lavrov has told the United States that Gershkovich was caught red-handed while trying to obtain secrets.

The United States on Monday determined that Russia had ”wrongfully detained” Gershkovich, effectively saying that espionage charges are bogus and that the case is political.

Many US reporters left Russia after President Vladimir Putin ordered troops into Ukraine last year - and more have left since the detention of Gershkovich.

The United States has repeatedly told its citizens to leave Russia due to the war in Ukraine and the risk of arbitrary arrest or harassment by Russian law enforcement agencies.